Container that I can loop through and access elements via key? C++

Question

Is there a container that I can access its element via key AND position?

Pretty much, is there some sort of mix between elements and vectors/deques..?

Answer 1

There is no standard container type for this.

You could use a combination of a std::map for key access, and a std::vector for position access. If you wrap them together in one class with accessor functions, you can make sure that whenever you insert a new element, both indexes are updated, avoiding inconsistencies.

If you are happy to use the Boost library, it provides a convenience template for these kinds of things. It's called boost::multi_index, and it provides for a lot of flexibility, with many different ways to access the same underlying data.

An example of a combination along the lines of what you described, i.e. with string-keys as well as sequence position-based access, is found here.

The main data type is declared as

typedef multi_index_container<
  std::string,
  indexed_by<
    sequenced<>,
    ordered_non_unique<identity<std::string> >
  >
> text_container;

This defines an index with two access types: sequenced<> (i.e. by insertion position) as well as ordered_non_unique<identity<std::string>>, which is similar to a std::multimap<std::string,...>.